Count Semyon Romanovich Vorontsov (Russian: Семён Романович Воронцо́в; 26 June 1744 - 9 July 1832) was a Russian diplomat whose siblings included Alexander Vorontsov, Elizaveta Vorontsova, and Ekaterina Dashkova. He resided in Britain for the last 47 years of his life, from 1785 until his death in 1832, during which time he was the Russian ambassador to the Kingdom of Great Britain from 1785 to 1800 and to the United Kingdom from 1801 to 1806.
Semyon Vorontsov distinguished himself during the first Russo-Turkish War at Larga and Kagula in 1770. In 1783, he was appointed Russian minister at Vienna, but in 1785 was transferred to London. Vorontsov soon attained great influence and authority in Great Britain. Quickly acquainting himself with the characteristics of English institutions, with their ways and methods, he was able to render important services to his country. Thus, during the second Russo-Turkish War, 1787-1792 he contributed to bring about the disarmament of the auxiliary British fleet, which had been fitted out to assist the Turks; and in 1793 obtained a renewal of the commercial treaty between Great Britain and Russia. Over the next three years, he irritated Empress Catherine II with his vehement advocacy of the exiled Bourbons, sharp criticism of the Armed Neutrality of the North, which he considered disadvantageous to Russia, and denunciation of the partitions of Poland as contrary to the first principles of equity and a shock to the conscience of Western Europe.
On the accession of Paul I in 1796, Vorontsov was raised to the rank of ambassador extraordinary and minister plenipotentiary and was awarded immense estates in Finland. Neither Vorontsov's detention of the Russian squadron under Makarov in British ports nor his refusal, after the death of Alexander Bezborodko, to accept the dignity of imperial chancellor could alienate the favor of Paul. It was only when the emperor himself began to draw nearer to France that he began to consider Vorontsov as incompetent to serve Russia in England, and in February 1800 all the count's estates were confiscated. Alexander I on his accession in 1801 at once reinstated him, but ill health and family affairs induced him to resign his post in 1806. From that time till his death in 1832, he continued to live in London. He was buried in St Mary-le-Bow.
Besides his valuable Note on the Russian War and numerous letters, Vorontsov was the author of an autobiography and Notes on the Internal Government of Russia. His son Michael continued his father's Anglophile ways and was an eminent commander in the war against Napoleon and in the Russian subjugation of the Caucasus. His daughter Catherine married George Herbert, 11th Earl of Pembroke, 8th Earl of Montgomery.